Apparatus for controlling the speed of phonograph turntables



Feb. 6, 1945. R. L. STONE 2,369,085

APPARATUS FOR CONTROLLING THE SPEED OF PHONOGRAPHTURNTABLES Filed Dec. 2'7, 1943 AMPZ. lF/ER anym/rzswm 46 ,1 I o. AMPL l/ /f? Z35 "4NVENTOR. 252 303557 A. STONE 23, BY

AT T 031E) Patented Feb. 6, 1945 9 APPARATUS non CONTROLLING THE srnnn- Q or PHONOGRAPH TURNTABLES Robert L. Stone, Orange, Conn., assignor to. The Soundscriber Corporation, New Haven, Conn.,

a corporation of Connecticut Application December 21, 1943, Serial Ne.515, 6ss

'9 Claim.

This invention relates to phonographs, and more particularly to a dictating machine employing sound recording and sound reproducing apparatuses, and provided with a common amplifier which is adapted to be selectively switched from recording to reproducing'whenever desired.

One object of this invention is to provide a dictating machine or the above nature in which the sound waves are recorded at a low speed in closely-spaced grooves on a rotating disk record, such as was described in the prior patent, Reissue No. 22,183,-dated September 22, 1942, issued to Lincoln Thompson, entitled Apparatus for recording sound on thin disks.

A further object of the present invention is to provide an apparatus for equalizing the speed of rotation of the turntable, when reproducing,

to the speed at which the turntable was rotated during the recording process. This equalization is necessary because the recording head, which is heavierv than the playback head, introduces a greater drag upon the speed of.rotation of the record than does said playback head; consequently, the record will tend to rotate somewhat faster during playback andthereby impair the fidelity of voice reproduction.

A further object is to produce a device of the above nature which will be simple in construction,.inexpensive to manufacture, easy to install andmanipulate, compact, and very efficient and durable in use.

The present invention constitutes an improvement over the Disk dictating machine disclosed in the prior patent of Lincoln Thompson, No. 2,250,242, issued July 22, 1941.

With these and other objects in view, there have been illustrated on the accompanying drawing three forms in which theinvention may conveniently be embodied in practice. A

In the drawing,

Fig. 1 represents a schematic view of the first form of the invention, employing a smallelectromagnet embracing an aluminum disk, mounted upon the motor shaft, for the purpose of applying a drag thereon during reproduction.

Fig. 2 is a similar schematic view of the second form of the invention, in whichthe speed of the turntable induction motor is controlled by introducing a resistance into the circuit of a shaded pole on said motor w le reproducing.

Fig. 3 is a similar schematic of a third form of the invention, in which a resistance is inserted directly into the main circuit of the induction motor during reproduction, whereby the (Cl. ire-100.4)

equivalent to the greater drag of the recording stylus upon the record.

.In a dictating machine of the above nature it will be understood that it is'quite important that the record shall rotate at the same speed during recording and reproducing in orderto preserve the natural tone of the voice and produce maximum fidelity of reproduction.

Referring now to the drawing, in which like reference numerals denote corresponding parts throughout the several views, the numeral l0 (Fig. 1) indicates the casing of a motor, having a shaft ll, upon the bottom of which is mounted a circular aluminum disk l2. The top of the shaft H is provided with a pinion l3, meshing with a larger gear l4, which is adapted to drive a turntable 15 at a uniform speed by means of a shaft l6 secured to said gear It. The turntable l5 has a record disk ll mounted thereon. In order to record dictation, music, or other soundsupon the record disk l1, provision is made of a recording head i8 adapted to be swung at uniform speed across the record by a suitable feed mechanism (not shown). The recording head l8 has a stylus I! which plows an undu-- lating spiral groove in the surface of the record was it swings over the turntable toward the center thereof. The dictation recorded upon the 'record disk I1 is adapted to be reproduced by means of a playback head 46 having a stylus 2|,

which may be freely movable in the grooves of the record asdescribed in the Patent No.

2,250,242, mentioned above, or which may be pos-- itively driven across the record by a mechanism source of .A. C. current '24, which is converted into D. C. by means of a rectifier 25 having input terminals 26, 21, and output terminals 28, 29.

The terminal 28 is connected by means of a conductor 30 to a fixed resistance 3| of such size as to cause said electromagnet 22 to apply the proper drag upon the aluminum disk I2 equivalent to that applied to the recordl! on the turntable turntable speed will be reduced by an amount I5 by the recording stylus l8.

ing in Fig. 1 in neutral position, but being adapted to be moved either to the right or to the left to the dotted line positions 36, 31, as clearly shown. When the pointer is in the dotted line position 36, the machine will be in condition for recording, and when it is moved to the dotted line position 31, the amplifier will be connected rial previously recorded upon the record.

In order to control the circuit through the electromagnet 22, provision is made of a rotary switch arm 38 which is mounted rigidly upon the shaft 32 for rotation therewith, said arm being connected to the electromagnet 22 by a conductor.

38a. Provision is also made of a fixed contact 39 located in the path of the end of the movable contact arm 38. The contact 39 is connected by means of a conductor 40 to the terminal 29 of the rectifier 25.

A playback switch arm 4| is also rigidly mount l ed on the rotary shaft 32 for swinging in synchronism with the switch arm 38, and said switch arm 4 I is connected by means of a conductor 42 to an amplifier 43, as clearly shown in Fig. 1. The switch arm 4| is adapted to engage a fixed contact 44 whenever the pointer 35 is swung to the dotted line position 31, thus closing the circuit through the playback head 46, which is connected by a conductor 45 to the contact 44. A conductor 41 is also furnished for connecting the other side of the playback head 46 to the amplifier 43.

A playback arm 48 i mounted for swinging across the record, and said arm is connected by means of a laterally-playless leaf spring 49 to I the playback head 46, whereby no lateral back lash will be permitted in the movement of the playback head 46. A pair of conductors 50, 5| serve to connect the amplifier 43 selectively to the loudspeaker or microphone, according to the manual switching of the selector knob 33, as fully disclosed in the previously-mentioned Patent No. 2,250,242.

A pair of conductors 52, 53, leading to a source of A. C. current, are also shown connected to the amplifier 43. 1

Operation of the first form of invention operator desires to reproduce a record upon the turntable, it will only be necessary for him to turn the selector knob 33 in a clockwise direction to shift the pointer 35, from the dotted line position 36 to the dotted line position 31. The electromagnet 22 will thus be energized automatically in synchronism with the playback head 46, thus causing said electromagnet to eiiert a retarding force upon the aluminum disk I2 equivalent to the greater drag of the head I8 upon the record I1 during recording.

Second form of invention.

around which is wound a main coil II4 for energizing the core pieces III, H2. The main coil H4 is connected to a source of alternating current ,5 by means of a pair of conductors H6,

I I1, as shown.

In order to control the speed of the motor, provision is made of a shaded coil I I8 which is adapted to surround the core piece I I 2 and is connected in-circuit with 'a resistance I20 by means of conductors II9, I2I. The resistance I20 is also joined as by means of a conductor I22, to a movable rotary switch arm I23, which while recording, will to the pickup head for reproducing the mate- In operation, it will be seen that whenever the engage a fixed'contact I24 connected by a conductor I25 to a junction I26 between the conductor H9 and a wire leading to the resistance I26.

Provision is made of a switch operating shaft I21, similar to the shaft 32 of the first form of the invention (Fig. 1). The shaft I21 has a selector knob I28 on its extremity, having a pointer I29 associated therewith, said pointer being adapted to swing from the dotted line recording position |30to the dotted line play-back position I3I.

The shaft I 21 has a rotary playback switch arm I32, connected by a conductor I33 to one input terminal I34 of an amplifier I36, the other input terminal being indicated by the numeral I35. A pair of conductors I31, I38 are connected to the amplifier I36 for introducing a loudspeaker or a microphone selectively into the circuit thereof. l

A stationary switch contact I39 is joined by a conductor I46 to a playback head I4I which is also connected by a conductor I42 to the amplifier terminal I35, as shown. The numeral I43 indicates a playback arm which is connected to the pickup head MI by a' leaf spring I44, similar to the leaf spring 49 of th first form of the invention.

Operation of the second form of invention In the operation of the second form of the invention the resistance I20 will be automatically inserted into the circuit of the shaded pole I I8 whenever the selector knob pointer I29 is swung from the position I36 to the position I3I. The desired speed reduction is thereby introduced to equalize the speed of reproducing to that at which the record was recorded.

Third form of invention In the third form of the invention, illustrated the current source 2|5 by a conductor 2H, and

said resistance 2|8 is shunted by a circuit including a wire 2I9, a rotary switch arm 220, a fixed cbntact HI and a conductor 222.

The junction between the connector 222 and a wire leading to the resistance 2I8 i connected to the main coil 2 I 4 by means of a conductor 22211. The rotary switcharm 220 is mounted to rotate with a shaft 223 having at one end a selector knob 224 similar to the knobs 34 and I28 described above, andhaving a pointer 225 associated therewith. The pointer 225 is adapted to be swung from the dotted line recording position 226 to the dotted line playback position 221.

Mounted upon the shaft 223 is a rotary playlar to the playback arms 48 and H3 described 1 heretofore, is connected by means of a leaf spring 240 to the playback head 234.

Operation of the third form of invention In the operation of the third form of the invention, it will be understood that when the selector pointer 225 is turned from the position 226 to the position 221, for-shifting from recording to reproduction, the shunt circuit through the resistance 2|8 will be opened, throwing the resistance 2|8 directly into the circuit of the main coil 2. The speed of the motor will thus be reduced suillciently to render the turntable speed equal to that at which the record wa recorded.

While there have been disclosed in this specification three forms in which the invention may be embodied, it is to be understood that these forms are shown for the purpose of illustration only, and thatthe invention is not to be limited to the specific disclosures, but may be modified and embodied in various other forms without departing from its spirit. In short, the invention includes all the modifications and embodiments coming within the scope of the following claims.

Having thus fully described the invention, what is claimed as new, and for which it is desired to secure Letters Patent, is:

1. In a dictating machine, a turntable for supporting a disk record, a motor for driving said turntable at constant angular speed, said motor having a shaft,a metallic brake disk secured to said shaft for rotation therewith, an electromagnet located adjacent said metallic disk, a styluscarrying recording head and a stylus-carrying playback head of lighter .weight than said recording head mounted for swinging movement over said record, and means for simultaneously energizing said playback head and said electromagnet to cause the latter to exert a retarding force upon said metallic disk during playback equal to the difierence in drag of said recording and playback heads on said record.

2. In a dictating machine, a turntable for supporting a disk record, a motor for driving said turntable at constant angular speed, said motor having a shaft, a metallic brake disk secured to said shaft for rotation therewith, an electromagnet embracing said disk, a recording head mounted to swing across said record during recording, 9, playback head of lighter weight than said recording head mounted to swing across said record during playback, and means for energizing said electromagnet during playback to retard said motor and equalize the speed of the record during playback to the speed of the record during recording.

3. In a dictating machine, a sound record, a recording head and a playback head of lighter weight than said recording head resting upon said record, means for driving said record comprising an induction motor having a, stator core.

saidv motorhaving a shaded coilsurrounding a portion ofv said core, an electric circuit including saidshaded coil, an electric circuitincluding said playback .head andpan amplifier, and 1 manually operated switch means to simultaneously close said playback head circuit and tointroduce an impedance into said shaded coil circuit, whereby said shaded coil during playback will be caused to retard the speed of said motor and equalize it to that at which the record was recorded.

4. In a dictating machine, a sound record, a

recording head movable over said record during recording, a playback head of lighter weight than said recording head movable over said record during playback, means for driving'said record comprising an induction motor having a stator core, a main coil embracing said core, a circuit including said main coil and an impedance, means to nullify said impedance during recording, and manually-operated means to introduce said impedance into said motor coil circuit during playback in order to retard the speed of said motor during playback so as to render it equal to that at which the dictation was recorded.

5. In a dictating machine, a driven sound record, a, recording head movable over said record during recording, a playback head of lighter weight than said recording head movable over said record during playback, means for driving said record comprising an induction motor having a stator core, a, main coil embracing said core, a circuit including said main coil and a resistance, means to nul ify said resistance during recording, and manually-operated means to introduce said resistance into said motor coil circuit during playback in order to reduce the speed of said motor during playback and render it equal to that at which the dictation was recorded.

6. In a dictating machine, a sound record driven at constant angular speed, a recording head movable across said record during recording, a playback head of lighter weight than said recording head movable across said record during playback, andmeans to reduce the speed of said record during playback to the speed of the record duringrecording.

7. In a dictating machine, a sound record driven at constant angular speed, an amplifier, a recording microphone, a reproducing loudspeaker, means for selectively shifting said amplifier to said microphone or said loudspeaker, respectively, a recording head connected with said amplifier and movable across said record during recording, a playback head of lighter weight than said recording head connected with said amplifier and movable across said record during playback, and

more speed-reducing drag upon said record than I said playback stylus, a metallic brake disk on said driving shaft for rotation therewith, a magnet having a field embracing the rim of said brake disk, means to cause th field of said magnet to be applied during playback only, in order to retard the speed of said record so that it will b substantially equal to the recording speed.

9. In a dictating machine, a movable sound record, means to drive said record continuously, a

recording stylus and a playback stylus for engaging said record selectively, said recording stylus exerting a greaterspeed-reducing drag on said record than said playback stylus, a magnetic v brake for said drive means for applying a drag aaeaoes 

